Funny note, every one who is HIV positive also has antibodies against HIV. Testing for those antibodies were how the original HIV tests worked. They looked for the antibodies to prove you had the virus.
Antibody testing is how we diagnose many infectious diseases. There are a number of infections that are incredibly difficult to grow in a lab (viruses are notoriously hard to grow), so we have to find other ways to diagnose them. Take Lyme disease, for example: Borrelia burgdorferi (the bacteria that causes Lyme disease) is incredibly difficult to grow in a lab. It's also very expensive to do the PCR test to detect pieces of Borrelia burgdorferi. Most people diagnosed with Lyme disease are diagnosed by finding antibodies against the bacteria.
Funny note, every one who is HIV positive also has antibodies against HIV. Testing for those antibodies were how the original HIV tests worked. They looked for the antibodies to prove you had the virus.
Antibody testing is how we diagnose many infectious diseases. There are a number of infections that are incredibly difficult to grow in a lab (viruses are notoriously hard to grow), so we have to find other ways to diagnose them. Take Lyme disease, for example: Borrelia burgdorferi (the bacteria that causes Lyme disease) is incredibly difficult to grow in a lab. It's also very expensive to do the PCR test to detect pieces of Borrelia burgdorferi. Most people diagnosed with Lyme disease are diagnosed by finding antibodies against the bacteria.